A. Field of the Invention
The present invention relates to a novel perpendicular magnetic recording medium to be loaded on a variety of magnetic recording apparatuses and a novel method of manufacturing the perpendicular magnetic recording medium according to the present invention.
B. Description of the Related Art
Perpendicular magnetic recording technology has recently attracted a great deal of attention from concerned parties as a practical technology for realizing a magnetic recording process with higher density, in place of the conventional longitudinal magnetic recording format.
Basically, any of the perpendicular magnetic recording media comprises the following: a magnetic recording layer made from a hard magnetic material, an underlayer for orienting the magnetic recording layer in a specified direction, a protective film for protecting the upper surface of the magnetic recording layer, and a back-lining layer made from a soft magnetic material, which functions to concentrate the magnetic flux generated by a magnetic head used for executing a recording process onto the magnetic recording layer.
It has been a conventional practice to mainly apply a variety of alloys comprising CoCrPt, CoCrTa, or the like as the material for constituting a magnetic recording layer to be used for a perpendicular medium. When any of these alloys is used, since chromium (Cr) is a non-magnetic material it segregates itself within the grain boundary, and individual grains are magnetically dissociated from each other. This generates specific physical characteristics in terms of the high coercive force (Hc) essentially required for the magnetic recording medium. Segregation of chromium toward grain boundaries has thus been facilitated by devising a process for forming a film used for the longitudinal medium by heating it or adding bias to a substrate. Nevertheless, as in the case of treating the longitudinal medium, even after applying a heating process or adding bias to the substrate, the actual amount of the segregated chromium component remains negligible in the case of processing the perpendicular medium. This in turn increases the occurrence of a noise component therein, resulting in a problem.
To solve this problem, a magnetic recording layer comprising an alloy of CoPtCrO that is capable of facilitating magnetic dissociation of grains by causing oxide to be segregated into grain boundaries has been proposed (see S. Oikawa et al. “High performance CoPtCrO single-layered perpendicular media with no recording demagnetization,” IEEE Trans. Magn, Vol. 36, pp. 2393-2395, 2000). In addition, a further proposal has been made of a granular medium applied with a magnetic recording layer made from an alloy of CoCrPt—SiO2 (see T. Oikawa, et al. “Microstructure and Magnetic Properties of CoPtCr—SiO2 Perpendicular Recording Media,” IEEE Trans. Magn, Vol. 38, pp. 1976-1978, 2002).
For example, when a granular film comprising an alloy of CoCrPt—SiO2 is formed, a segregation process is advanced by causing the SiO2 component to surround the periphery of grains made from the alloy of CoCrPt, thereby causing individual grains of the CoCrPt alloy to be dissociated magnetically. Thus, in the case of forming the granular film, instead of applying phase separation (separation of magnetic phases) of the above-mentioned alloy material, an insoluble amorphous material such as oxide or nitride is added to a specific alloy material.
According to the report from the above-mentioned document, it was confirmed that, unlike the case of a conventional recording medium comprising a magnetic recording layer made from a CoCr alloy component, the above granular medium proved to have reduced the occurrence of noise components in itself. This granular medium thus shows the promise of generating significant future demand.
On the other hand, in the case of forming the granular film by heating its substrate, oxidation or nitrification of the Co component or intermingling the phase of alloy components with the phase of non-magnetic alloy components may cause a problem. To prevent this, the granular film must be formed with no pre-heating process. However, when the granular film is formed without heating, noise components cannot be fully eliminated from the granular medium because of insufficient dissociation between the phases of alloy components and non-magnetic alloy components. Further, another problem is that the uniaxial anisotropy constant (Ku) value of the granular film is lowered by the generation of stacking faults in the alloy phase, which eventually results in total loss of thermal stability.
A method of forming a magnetic recording layer (or a protective film) without applying any thermal treatment and then subsequently thermally treating the granular film at high temperatures ranging from 400° C. to 600° C. after the layer or film has been formed has been practiced to solve the above problems. For example, Laid-Open Japanese Patent Publication No. 2000-306228 proposes that by providing thermal treatment at a minimum of 400° C. for a duration ranging from 5 minutes to 60 minutes (or according to Laid-Open Japanese Patent Publication No. 2000-311329), at 250° C. to 500° C. for a duration of 0.1 to 10 hours), it is possible to secure a granular medium capable of executing a magnetic recording operation with high density through sufficient dissociation between the non-magnetic matrix material and magnetic grains contained in the granular medium. However, inasmuch as either of the above techniques requires thermal treatment at very high temperatures for long periods, neither of them is feasible for mass production of the granular medium.
The inventors of the present invention have thus far reported that it is possible to improve the orientation characteristics of a magnetic recording layer, decrease the initially grown layer in the magnetic recording layer, and reduce grain size by forming a ground layer comprising a material made from soft magnetic permalloy and applying Ru or a Ru-based alloy for constituting a non-magnetic intermediate layer, thereby enabling the acquisition of a novel medium incorporating outstanding magnetic characteristics and read-write performances (according to the Laid-Open Japanese Patent Publication No. 2002-358617, No. 2003-123234, and No. 2002-367160).
The present invention is directed to overcoming or at least reducing the effects of one or more of the problems set forth above.